jo7b01540_si_002.cif (1.7 MB)

Laterally π‑Extended Dithia[6]helicenes with Heptagons: Saddle-Helix Hybrid Molecules

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posted on 2017-07-07, 00:00 authored by Takao Fujikawa, Yasutomo Segawa, Kenichiro Itami
A laterally π-extended dithia[6]­helicene 1, representing an interesting saddle-helix hybrid molecule containing an unusual heptagon, has been synthesized by MoCl5-mediated oxidative stitching of tetrakis­(thienylphenyl)­naphthalene precursor 2 involving reactive-site capping by chlorination and subsequent Pd-mediated dechlorination of tetrachlorinated intermediate 1-Cl4. Highly distorted, wide helical structures of dithia[6]­helicenes (1 and 1-Cl4) were clarified by single-crystal X-ray diffraction analyses where heterochiral slipped π–π stacking was displayed in a one-dimensional fashion. Notably, theoretical studies on the thermodynamic behavior of 1 predicted an extraordinarily high isomerization barrier of 49.7 kcal·mol–1, which enabled optical resolution and chiroptical measurements. Electronic structures of these huge helicenes were also examined by photophysical and electrochemical measurements.